In an in-service load test, instrumentation is used to measure the response of the bridge due to ambient traffic over a specified amount of time. Diagnostic load tests are used to quantify a bridges response to heavy loads, and the response is then used to either directly evaluate the bridge or calibrate a numerical model which is in turn used to evaluate the bridge.
If the load crosses the bridge without damage and within the designated acceptable stress range, it was deemed as proof the bridge can carry the load. A truck, weighing the load the bridge is intended to be able to carry safely, crosses the bridge. Proof load tests are used in verifying the load carrying capacity of the bridge. A load, typically a heavily loaded vehicle, is then placed or driven across the bridge and the bridge response is measured.īridge load tests are often categorized into the categories of (1) proof tests, (2) diagnostic tests, and (3) in-service tests. In a bridge load test, instruments such as strain gauges tilt meters, deflection devices, or other instruments are strategically located and attached to the bridge.
Other evaluation methods can be used, along with visual techniques, to improve the load rating process such as non-destructive evaluation technologies of bridge load testing. The data generated from observational inspections are qualitative and rely on the inspector's experience, skill, and primarily focus on components of the bridge that can be readily seen. Inspections results and ensuing evaluations are used to classify the physical and functional condition of the bridge. In order to ensure the structural integrity of a bridge throughout its life, it is essential that the structural components of the bridge are routinely inspected and evaluated. This in turn has provided the opportunity to develop a process for conducting future biennial tests to and adding their results to an evolving database, thereby enhancing DelDOT's ability to operate and maintain the bridge. The results of this extended set of diagnostic load tests have enabled the bridge's baseline performance to be rigorously established.
This paper presents results from a unique series of six diagnostic load tests which have been performed over the first 6 years of the bridge's service life (just prior to the bridge's opening, and then again at 6 months, 1, 2, 4, and 6 years). The system, which not only collects data continuously during normal operation, has also been utilized during regularly scheduled controlled diagnostic load tests being used to monitor ongoing bridge performance. The SHM system is a fiber-optic based design with more than 120 sensors of varying type distributed throughout the bridge.
From the very early stages of the design process, the Center for Innovative Bridge Engineering (CIBrE) at the University of Delaware (UD) worked with the Delaware Department of Transportation (DelDOT) and their design-build team of Skanska and AECOM to plan and install a comprehensive structural health monitoring (SHM) system. The Indian River Inlet Bridge (IRIB), a 533-m long cable stayed bridge, was opened for traffic in 2012. One possible approach to reducing the cost while simultaneously improving the process is by utilizing structural health monitoring (SHM) systems to enable diagnostic load tests to be regularly and efficiently conducted. The management and maintenance of cable-stayed bridges represents a major investment of human and financial capital.